MIXTURES OF ELECTROLYTES MACGREGOR. 117 



1 per cent, and for the most part considerably less, are one half 

 positive and one half negative, and that whether the solutions 

 are arranged in the order of conductivity , or in the order of 

 mean concentration, they exhibit quite a sufficient alternation of 

 sign to warrant the conclusion that they are due chiefly at least, 

 to errors in tbe observations and in the graphical portion of the 

 calculations. 



In the case of the stronger solutions, Nos. 16-18 and 19-22, 

 the alternation of sign has disappeared. In the weakest solutions 

 of these two series, the differences are positive and small ; but 

 as the concentration increases, the differences become negative 

 and take increasing negative values, the negative difference 

 having its greatest value in No. 22, which is a mixture of a 

 strong solution of Na Cl with a saturated solution of K Cl. The 

 tendency towards a negative difference as the concentration 

 increases, may be recognised also in Nos. 11 and 15 ; and it is 

 perhaps worth noting that while the mean value of the positive 

 differences is slightly greater than that of the negative differences 

 up to a concentration of 1 gramme-molecule of salt per litre, the 

 mean negative difference is the greater for higher concentrations. 



It is manifest from these results that for solutions of these 

 chlorides containing less than say 2 gramme-molecules per litre, 

 it is possible to calculate the conductivity very exactly, but that 

 for stronger solutions the calculated value is less than the 

 observed. 



The jxcess of the observed over the calculated conductivities, 

 shews one or more of the assumptions implied in the mode of 

 calculation to be erroneous. It would seem to be probable that 

 the error is at any rate largely due to the assumption that the 

 molecular conductivity of an electrolyte at infinite dilution is 

 the same whether it exists in a simple solution or in a mixture, 

 and that the discrepancy is thus due to the effect of mixing on 

 the velocities of the ions. The mode of calculation assumes that 

 in the mixture the constituents are not really mixed, but lie side 

 by side, so that the ions of each electrolyte in their passage from 

 electrode to electrode travel through the solution to which they 

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